THE STUDY OF THE EVOLUTION OF THE ELOWEE. 293 



4 



become definitely fixed or not : as in Lonicera^ where the majority of the ovules 

 habitually abort ; in Polyosma, where, according to Blume, only one of the numerous 

 ovules forms a seed ; in Liquidambar, where the lowermost ovules are stated to be 

 always sterile ; in Aralia and Cori/lopsis, where one of a pair, and in Qalsqualis, where 

 one of three ovules is sterile. And, finally, cases occur, exemplified by Symplioricarpus, 

 where the sterility of particular ovules is no longer a matter of circumstance, having 

 become fixed and hereditary. 



Sterilization proceeding to an extreme leads to uuisexuality ; thus in the Hamameli- 

 daceae series exist between forms in which the ovary may or may not be sterile, to 

 others with definitely polygamous flowers and others where the unisexual condition is 

 attained ; in Nyssa, series can be traced between hermaphrodite and female flowers 

 owing to the loss of stamens ; in Griselinia, Aucuha^ and Garrya rudiments of the absent 

 sex are retained, but the last traces have disappeared in Ilclwingia and in the male 



flowers of Davidia. 



A crreat deal of lisrht has been thrown on the series just enumerated by the results 



^.^^yj ^.^^^ ^. ^*-, 



obtained in the experimental fields of enquiry. De Vries *, by his analysis of 

 ever-sporting varieties, was able to show how profoundly the environment affects 

 development. Here the primordium of the flower in Polycephalic Poppies was 

 influenced by changed conditions applied within the fifth or sixth week after the 

 beginning of germination, and fewer anomalous stamens were produced than under 

 normal conditions, w^hilst the occurrence of polycotyly and polycephaly in polycotylous 

 and polycephalous half-races did not become definitely fixed during cultivation and 

 selection. The phenomena concerned variability, not mutability. He f also found that 

 the development of the anther and pollen in (E. sointillmis was dependent on external 

 conditions to a hi^h decree. De Vries's ± (Enothera mutants show clearly grades of 



O" --3 



sterility. Some are rich in pollen, w^hilst scintlllans is poor; others form many seeds, 

 some few, as in elliptica, whilst in hrevistylis many plants set no seed at all, but he 

 believes the degree of fertility in many mutants will ultimately be found to follow 

 Quetelet's law of fluctuating variability. Finally, with regard to sex sterility, 

 uuisexuality is exhibited by ever-sporting varieties, mutants, and Mendelian hybrids. 

 R. P. Gregory § records that no stamens occur in one of the double forms thrown off by 

 Frimula sinensis ; and E. R. Saunders || has shown that the gyncjecium in double 

 Petunias is more or less deformed and when fertilized yields no seed, whilst double ^ 

 stocks are always sterile and are always obtained from seed set from ever-sporting 

 singles. De Vries ** obtained a male sterile mutant, (Enothera lata. Lastly, Batesonft, 

 Punnett, and Saunders, working with Sweet Pea, and SalamantI, with Potato, have 

 isolated male-sterile Mendelian forms. 



* H. De Vries, ' Species and Varieties ' (1905) 369, and ' Matation Theory,' ii. (1910) 313, 450. 



t H. De Vries, ' Mutation Tlieory/ i. (1910) 3S3. 



t H. De Vries, I.e., scintillans, ^<83 -J elliptica , 396; hrevistylis, 316. 



§ 



it 



(1911) 



•* H. De Vries, I. c. 409. 



Eedcliffe iS". Salaman, in Journ. Linn. Soc., Bat. xxxix. (1910) 301. 



